In the end they found only one sick cow — only one out of 36 million slaughtered last year.
But to many people, even that single case was scary news. It dominated the headlines when the Department of Agriculture announced the case in Washington State on Dec. 23.
It could have been a major crisis for the nation's food system, but the government stepped in, quickly, with a carefully-prepared message: It's … just … one … animal.
"Despite this finding, we remain confident in the safety of our food supply," said Secretary of Agriculture Ann Veneman at her first news conference.
Mad cow disease affects the brain and spine of an animal. The government said it had already moved, years ago, to keep those parts from grocery stores and restaurants. They said even if one sick cow slipped through, meat that did not come in contact with brain tissue was safe. The department added that 38,000 pounds of beef from the infected animal's herd were recalled, even though there were no signs that other cows were diseased.
The campaign to calm the public clearly worked. Industry associations say that after some initial hesitation, Americans have gone on buying beef. On Wall Street, the stock prices of major beef producers and buyers, such as McDonald's and ConAgra, are near 52-week highs.
Are You Safe?
Most public-health experts contacted by ABCNEWS say they believe the American public is generally safe from mad cow. They say the United States is very unlikely to suffer a repeat of the crisis that befell Britain in the 1990s, when the disease was not yet understood and 140 people died.
There is no evidence that any Americans have been infected, though the disease is slow to progress.
But that does not mean everyone is reassured.
"The odds are low, but I think the public thinks the odds are zero," said Felicia Nestor, director of the Food Safety Program at the Government Accountability Project, a watchdog group. "And to the extent that they believe that, they're wrong."
Nestor's group often hears from field inspectors from the Agriculture Department, who have concerns about food safety but fear for their jobs if they complain. Nestor says some of them complain they are not given enough training to spot an animal with mad cow disease, known medically as bovine spongiform encephalopathy, or BSE.
Consumer advocates call for increased chemical testing, to screen meat for telltale signs of infection.
"With more testing we could make those odds a whole lot lower," said Nestor.
John Stewart would like more testing too. He is CEO of Creekstone Farms, a beef processing company in Arkansas City, Kan., which, he said, has been losing $100,000 a day since the sick cow was reported.
Creekstone's problem is that it sells much of its meat overseas, and 50 countries have closed their borders to American beef. Some of them, such as Japan, insist that every single slaughtered animal be tested for the disease before its meat can go to market.
"Can there be another case of BSE in the United States?" said Stewart. "Of course there could. Will there be? Who knows?"
There are testing kits that can give quick indications as to whether an animal carries BSE. They are used in other countries, but the U.S. Agriculture Department has not yet approved any of them, saying it wants to make sure they are reliable.
Creekstone — breaking ranks with larger beef processors — offered to mollify its overseas customers by paying for testing itself. It has not gotten an answer from Washington.
"Waiting, or not doing anything, we believe, is not prudent," said Creekstone's Stewart. "We think this is something that should be dealt with swiftly."
The Department of Agriculture answers that it is taking tough steps:
It says it will test 40,000 cows for the disease — double what it did last year.
It says any so-called "downer" cows — animals sick enough that they cannot walk — will be removed quickly from the food supply. Inspectors did not have instructions to do that before December.
It has tightened standards for animal feed, so that one cow cannot get the disease from another.
Washington is using these measures as it negotiates with other countries, trying to get them to reopen their markets to beef from the United States. Mexico agreed on Wednesday, and others may soon follow.
"I think we have really put in place all the things that need to be done to assure the public that the meat supply is safe," said Bobby R. Acord, administrator of the Agriculture Department's Animal and Plant Health Inspection Service.
But that is not the end of the matter. An international panel — convened by the Agriculture Department — said it is quite possible that if one cow slipped through the cracks, there may be others.
And despite all the government's assurances, there is no saying people will be calm if another case makes headlines.